Locking cylinder



April 13, 1965 Filed May 27, 1965 R.'K. ANDERSEN ETAL 3,177,780

LOCKING CYLINDER 2 Sheets-Sheet 1 Vl/Mraz ;@ayer Affi/effe Car/ 1Q,Qafemdn April 13, 1965 R. K. ANDERSEN ETAL. 3,177,780

LOCKING CYLINDER Filed May 27, 1963 2 Sheels-Sheetl 2 l llll UnitedStates Patent Office 3,177,780 Patented Apr. 13, 1965 anims@ LOCKINGCYLINDER Roger K. Andersen, 2655 226th St., Torrance, Calif., and i CarlP. Roseman, 400i) Vista Court, 'La Crescenta,

Calif.

Filed May 27, 1963, Ser. No. 283,402 l5 Claims. (Cl. 92-24) Thisinvention relates to an extensible and retractable hydraulic actuatorcomprising a cylinder and piston therein and is particularly directed tomeans for automatically locking the piston at at least one of its limitpositions. Such a locking means typically automatically latches andlocks the piston in response to arrival of the piston at the limitposition and subsequently automatically releases the pistonl in responseto the application of fluid pressure in a direction to shift the pistonaway from the limit position.

One important problem met by the invention is to provide acircumferential series of latching fingers that are of simpleconstruction, easy to fabricate, but at the same time are of rugged highstrength `construction to withstand axial forces of high magnitude. Inmany devices of this type, the latching fingers are constructed byslitting one end of a sleeve, the base ends of all of the lingers beingintegral vwith each other. One disadvantage of such a construction isthe time, care, and expense involved in cutting the longitudinal slots.A more serious disadvantage is that since the fingers swing by flexingaction, they must be relatively thin for the required flexibility andtherefore are of limited tensile strength. In other devices of thistype, independent fingers are employed but are not shaped andconstructed for resistance to high magnitude forces.

The present invention meets this problem by employing relatively massivefingers which are aligned parallel with the axis of the cylinder land,therefore, are subject to mainly longitudinal tensile stress. Each ofthe individual lingers lhas an end enlargement at one end Whichfunctions as a bearing portion for pivotally anchoring the linger, andeach of the fingers has a flange at its other end to serve as la latchelement. Both the end enlargement and the end flange `are stressed inshear when the lingers engage the piston, but both are of massiveconstruction for high strength, and the shear forces are longitudinalforces lying close to the bodies of the fingers.

ln the preferred practice of the invention, the circumferential set oflatch fingers are of the shape of longitudinal sections severed from acylindrical configuration by longitudinal radial saw cuts, thecylindrical configuration having a generally ring-shaped enl-argement atone end and a flange eat the other end. The sections of the ring-shapedenlargement constitute bearing portions of the individual lingers, andsections of the end flange constitute latching elements on the ends ofthe individual fingers. Spacer members of substantially the same crosssection as the end enlargements may abut the bearing portions of thengers and space the fingers apart.

The invention is further directed to the problem of biasing the lingers.As will be explained, in some practices of the invention, the fingersare biased by means exerting pressure against the heels or hearing endsof the lingers. In `one example, `spring means exerts the required endpressure, and in another example the fluid that actuates the piston isemployed to exert the required end pressure. In another practice of theinvention, the fingers are .biased outward by `a multiple-tum coilspring with the circumferential set of lingers embracing the coilspring.

One practice of the invention is further characterized by the provisionof means to detect and indicate when the piston is at a limit position.As will be explained, a feature of the invention is the concept ofemploying a reciprocating locking sleeve for this purpose.

The features and advantages of the invention may be understood byreference to the following detailed description and the accompanyingdrawings.

In the drawings, which are to be regarded as merely illutsrative:

FIG. l is a longitudinal sectional view of one embodiment of theinvention;

FIG. 2 is a perspective diagrammatic view showing how thecircumferential set of latching lingers correspond to longitudinalsegments of a cylindrical configuration with spacers between the bearingpor-tions of the successive latching fingers;

FIG. 3 is a perspective view of one of the latching fingers employed inthe first embodiment of the invention;

FIGS. 4 and 5 are fragmentary plan views of a latching linger and anassociated pressure-applying means showing how the pressure-applyingmeans creates a moment for biasing the finger;

FlG. 6 is a sectional View illustrating a second embodiment of theinvention;

FIG. 7 is a sectional View illustrating ya third embodiment of theinvention; and FIG. 8 is a perspective view of a latc'hinlg lingeremployed in the third embodiment of the invention.

The lirst embodiment of the invention shown in FIG. l includes lacylinder lll and a piston, generally designated l2, slidingly mounted inthe cylinder, the piston being mounted on one end of a piston rod 14 forextending and retractng the piston rod in a well known manner. Thepiston l2 is an assembly comprising a piston body l5 with a radial web16 and two bushings 1S and 20 on opposite sides of the web. This pistonassembly is mounted on a reduced `end portion 22 of the piston rod andis clamped against 'a circumferential shoulder 24 of the piston rod by anut 25. For sealing purposes the piston is provided with an outercircumferential O-ring 26 and the reduced end portion of the piston rodhas a` circumferential groove 2S confining a second O-ring 30.

The bushing 13 in cooperation with the piston body 15 forms a firstannular or ring-shaped cavity 32 for journaling the bearing por-tions3ft of a first set of latch fingers 35, which fingers are formed withlatch elements or shoulder-s 36 on their outer ends. In like manner, thebushing 2t) cooperates with the piston body l5 to form a second annularor ring-shaped cavity 3l; to journal the` 'bearing portions 3d-` of asecond set of latch fingers 35a which are identical to the lirst set.

The shape of the latch lingers 35 and 35a may be understood by referenceto FIG. 2 which shows in phantom a cylindrical member All with aring-shaped enlargement 42 at one end and a radial flange 44 at theother end, the ring-shaped enlargement extending radially inwardly ofthe cylindrical body and the radial flange 44 extending radiallyoutward. The latch fingers 35 are in effect longitudinal sections of thecylindrical body 40 produced by sawing the cylindrical bodylongitudinally to produce the individual latch `members with the latchmembers separated by longitudinal lrerfs or saw cuts 45. Thus thesections ofthe ring-shaped enlargement 42 are the bearing portions 34 ofthe latch fingers and the sections of the` radial flange 44 are thelatch elements 36 of the latch lingers. The successive latch lingers 35of the circumferential set are spaced apart by spacer members 46 whichare of the shape of sections of the ring-shaped enlargements 42 andwhich in practice may be simple disks sliced from a round rod.

As shown in FIG. l, the two sets of latch lingers 35 3,1 E and 35aextend through annular openings 4S of the two annular or ring-shapedcavities 32 and 58.

The latch fingers 35 coopenate with a fixed latch ring 50andfarreciprocative locking sleeve 52. In like manner, the latch fingers35a cooperate with a fixed latch 'ring 54' at the other end of thecylinder and a second reciprocative locking sleeve 55. The latch ring 50is anchored between one end of the cylinder and an adjoining cylinderhead 56, and in like manner the second locking sleeve 55 1s clampedbetween the other end of the cylinder and a second cylinder head 58. Asshown in FtG. l, the cylinder head 56 is mounted on the cylinder itl byscrew threads, and the second cylinder head 53 is `anchored by a nut 6i)that has a radially inward fiange 62 in engagement with an outercircumferential rib 64 of the cylinder,

The locking sleeve 52 is provided with outer and inner O-rings65 and isurged from a release position to a locking position by a suitable coilspring 66. The second locking sleeve55 has an outer O-ring63 and isurged towards its` locking position by an lassociated coil spring 69. Atits locking position, locking sleeve 52 has a cylindrical locking flange7@ which engages the outer ends of the associated latch fingers 35 tohold the latch fingers against the corresponding latch ring Sti, as maybe seen in FlG. l, where the locking sleeve 52 locks the latch fingers35 in engagement with the latch ring Sti. In like manner, the secondlocking sleeve 55 has a circumferential shoulder 71 at its leading endto releasably hold the latch lingers 55a in engagement with the latchring 54. Each of the two locking rings 52 and 55 is retractable by fluidpressure, and for this purpose each of the two cylinder heads issuitably vented. Thus, the cylinder head 56 has a vent bore 72, and abore '73 in the cylinder head 58 is a vent in one of its functions. Thelocking y cylinder 52 is retracted by fluid pressure admitted into thecylinder 1@ on the corresponding side of the piston 12 by acorresponding port 74 at the corresponding end of the cylinder. In likemanner, the second locking sleeve 55 is retracted by fluid pressureadmitted through a second port 75 at the other end of the cylinder.

The locking sleeve 55 is provided with a stem 82 to permit the lockingsleeve to be manually retracted in opposition tothe pressure of thespring. The stem 32 extends through the previously mentioned vent bore73 and into an external slot 85 of the cylinder head 5S. The portion ofthe stem S2 that lies in the slot 85 is formed with a diametrical slot86 for operation by a manual lever 85. The lever 88 is fulcrumed on across pin 96 in the cylinder head slot 85, and one arm 92 of the leverextends into the diametrioal slot 86 of the stern 82. It is apparentthat the lever 88 may be manually operated to cause retraction of thelocking sleeve 55 when the fluid pressure in the cylinder 10 is too lowto overcome the spring.

It is essential that the two sets of latch fingers 55 and 35a besuitably biased radially outward for engagement with the 'two latchrings Si) and 54 respectively. In this first embodiment of theinvention, means is provided to exert biasing pressure against thebearing portions 34 of the two sets of ngers. For this purpose, a washer94 is mounted in each of the two cavities 32 and 38 contiguous to thebearing portions 34 of the two sets of latch fingers. The two washers 94are subjected to pressure selectively by a plurality of small auxiliarypistons 96 that are mounted in corresponding longitudinal bores 98 inthe web 16 of the piston body 15. Each of the auxiliary pistons'96 isprovided with an O-ring 10i) to make the piston responsive to fluidpressure differentials across the length of the longitudinal bores. Whenfluid pressure is applied to one side or the other of the piston 12, thefluid pressure acts on the corresponding ends of the auxiliary pistons96 to urge the auxiliary pistons against the corresponding washer 94,thereby to exert pressure against the bearing portions 34 of thecorresponding set of latch fingers.

The manner in which the latch lingers 35 and 55a are biased by thepressure of the two washers 94 may be understood by referring to FIGS. 4land 5 which show one of the latch fingers 35a in abutment with thecorresponding washer 94. When the latch finger 35a is perpendicular tothe face of the washer 94 and parallel with the axis of the cylinder1t), as shown in FIG. 4, the full width of the bearing portion 34 of thelatch finger abuts the surface of the washer 94. On'the other hand, ifthe latch linger 35a is forcibly swung radially inward from its normallongitudinal alignment, the two opposite ends 34a and 3412 of thebearing portion 34 of the latch finger rock backward against the Washer94 in opposition to the pressure applied to the washer. The vreason thatthe two ends of the bearing portion 34 rock backward against the washer94 may be understood when it is considered that the bearing portion 34is arcuate across its width and is rocked out of parallel relationshipwith the washer.

Associated with the locking cylinder 52 is an indicator switch 162having an operating plunger 164 that senses the position of the lockingcylinder. For this purpose, the locking cylinder 52 lhas an outercircumferential groove 165 into which the operating plunger or feeler104 extends when the locking sleeve is at its advanced or Vlockingposition shown in FIG. l. p Y

Associated with the second locking sleeve is a second indicator switch196 having an operating plunger or feeler 108 which responds to an outercircumferential groove 110 of the locking sleeve. Preferably, twoindicator lamps (not shown) controlled by the switches M2 and 166respectively are energized when .the locking sleeves are at theiradvanced positions locking the piston 12. Thus, the switch 162 is closedin FIG. 1 to indicate that the piston 12 is at the corresponding end ofthe hydraulic cylinder 1t) and locked.

Operation The manner in which the device functions for its purpose maybe understood from the foregoing description. In FIG. l, the piston 12is at its left limit position, yand accordingly the indicator switch 102is closed as heretofore explained. The latch fingers 35 are inengagement with the latch ring 5t) and are locked in their positions of:engagement by the locking sleeve 52, the cylindrical locking flange lilof the locking ring engaging the ends of the locking fingers to holdthem in their outward positions in a positive manner. Since the piston12 is mechanically secured at its left limit position in this manner,the fluid in the cylinder 1t) on the right side of the piston need notbe under pressure. If the Y of the looking sleeve abutting the latchringvl. TheV right hand indicator switch 106 is open, since its plungeror feeler 108 is not in register with the circumferential groove 110 ofthe locking sleeve.

lf the pressure is released in the cylinder on the right hand side ofthe piston 12 and uid under pressure is admitted through the left port74 to apply fluid pressure to the left side of the piston, the fluidpressure acting on the leading end of the locking sleeve 52 causes thelocking sleeve to retract in opposition to the force of the springk 68,thereby causing the locking sleeve to release the latch fingers 35. Atthe same time, the ii-uid pressure ac-ts on the left side of the pistonto initiate rightward shift of the piston away from its left limitposition. The pull on the latch fingers 35 by the piston causes thelatch fingers to be cammed radially inward by the latch ring 50 torelease the piston for its right- Ward movement. At the same time, theiiuid pressure on the left side of the piston 12. is communicated to theauxiliary pistons 96 to cause the auxiliary pistons to shift rightwardagainst the rightward washer 94 and thus bias the latch fingers atowards their latching positions.

As the piston 12 approaches the right hand latch ring 54, the latchfingers encounter the locking sleeve and retract the locking sleeveagainst the opposition of the corresponding coil spring 69. At the sametime, the latch fingers 35a are cammed radially inward by the latch ring54 until they pass the latch ring, whereupon the biasing force exertedby the auxiliary pistons 96 causes the latch rings to swing radiallyoutward to positions of effective engagement with the latch ring. Assoon as the latch fingers 35a engage the latch ring 54, the lockingsleeve 55 advances slightly under the force of the spring 69, theannular latching shoulder of the looking sleeve engaging the ends of thelatch fingers to hold the latch fingers in their latching positions in apositive manner.

The left indicator switch 102 opens when the fluid pressure on the leftside of the piston 12 causes the locking sleeve 52 to retract from theposition shown in FIG. 1, thereby moving the :groove 105 of the lockingsleeve out of register with the plunger or feeler 19S of the 4indicatorswitch. In the event that the pressure on the left side of the piston isreduced while the piston is away from its left limit position, thespring dS causes the locking sleeve S2 to shift rightward to a limitplosition at which a radial flange 114i of the flocking sleeve abuts thelatch ring Sii. At this advanced position of the locking sleeve, thegroove 195 is out of register with the operating plunger or feeler 163of the switch 1112 to cause the switch 162, to be open.

Before the rightwardly moving piston reaches the right locking sleeve55, the locking sleeve is in the position shown in FIG. l, and theindicator switch 1&6 is open. As soon as the locking sleeve is retractedby the piston 12 as the piston reaches its right limit position, thecircumferential groove 111i of the locking sleeve registers with theplunger or feeler 168 of the switch 196 to cau-se the switch to closeand thereby indicate that the piston is at its right limit position.

The second embodiment of the invention shown in FIG. 6

FIG. `6 illustrating a second embodiment of the invention is largelysimilar to FIG. 1, as indicated by the l latch lingers are biased byspring pressure, whereas 1n the previously described FIG. 1 the llatchfingers are biased by fluid pressure.

in FIG. 6 the piston 12a has a piston body 15o with a radial web 16a.The piston assembly provides a cavity 1213 to journal the latch lingers35 and provides a second cavity 122 to journal the latch fingers 35a.Associated with each of the two sets of latch ngers is a previouslydescribed washer 94, and each washer is subjected to continuous pressureby a pair of Belleville washers 124 whch are positioned back to bachunder axial compression in the manner shown. Except for the manner inwhich the latch fingers 35 and 35a are biased by the Belleville washers124, the second embodiment of the invention functions in the same manneras the first described embodiment.

The third embodiment of the invention shown in FIG. 7

FIG. 7, illustrating the third embodiment of the in Vention, shows apiston 12b which includes a piston body 15b having a radial web 15b, thepiston body being provided with an outer circumferential O-ring 125 andan inner circumferential O-ring 1126. The radial web 1617 is backedagainst a circumferential shoulder 128 of a piston rod 14h and isclamped against the shoulder by a nut 131i. The Vnut 13@ is of taperedconfiguration as shown, and the piston rod 14,5 has a flared portion 132adjacent the cincumferential shoulder 123, which iiared portion is ofthe same taper as the nut 130. The flared portion 132 of the piston rodcooperates with the piston body 15b to form an annular cavity 13d forjournaling a first set of latch fingers 135, and the 'tapered nut 13)cooperates with the piston body to form a second annular kcavity 136 tojournal a second similar set of latch fingers g.

The latch fingers 13S are, in general, similar to the previouslydescribed latch fingers 35 but differ in that the bearing portions 138of the latch fingers protrude radially outwardly instead of radiallyinwardly. Thus, the bearing portions 13S as well as the latch elements15st) of the latch fingers are on the outer sides of the .latch fingers.

rlhe annular cavities 134 and 136 are of generally ring-shapedconfiguration, as heretofore described; but since the bearing portions133 are on the outer sides of the latch fingers, the bearing portionsmust be cut away or relieved to give the latch fingers the requiredfreedom for pivotal movement in the cavities. FlfG. 8 shows how each ofthe bearing portions 138 is cut away or relieved to form four faces 142.

in this third embodiment'of the invention, each of the two sets of latchiingers 13S and 135s is biased radially outward by a multiple turn coilspring 144. Preferably, each of the latch fingers is formed with agroove on its inner side, as best shown in FIG. 8, for the purpose ofengaging the corresponding coil spring 144. The two sets of latchfingers embrace the two coil springs 14d, as shown, with sufficientsnugness to cause the coil springs to bias the fingers towards theirlatching positions. An important feature of this construction is thereliability of the two coil springs 142.1 for their biasing action. ifone of the coil springs 144 is broken, the coil spring will still serveas a biasing means as long as a fuil turn or nearly a full turn of thecoil spring is intact.

it is apparent that in all three embodiments `of the invention the latchlingers are of exceptionally rugged construction of and capable ofwithstanding exceedingly high forces both in tension along the length ofeach latch finger and in shear at each of the two ends of the latchfinger.

Our description in specific detail of the selected embodiments of theinventionv will suggest various changes, substitutions, and otherdepartures from our disclosure within the spirit and scope of theappended claims.

We claim:

1. ln a fluid-pressure actuator having a cylinder member and a pistonmember reciprocable axiaiiy therein, means for locking the piston at alimit position in said cylinder comprising:

a circumferential set of discrete latch fingers of curved transversecross-section of the shape of longitudinal sections severed from acylindrical configuration by longitudinal radial saw cuts, saidcylindrical configuration having a concentric, generally ring-shapedenlargement .at one end and a flange at the other end, the sections ofthe enlargement constituting bearing portions of the individual fingersand the sections of the flange constituting latch elements of theindividual fingers;

means fixed relative to one of said cylinder member and piston memberand forming a circumferentially continuous generally `ring-shaped cavityconfining and journaling said bearing portions of the fingers forswinging movement of the fingers;

latch means fixed relative to the other of said cylinder member andpiston member to engage said latch elements to releasably anchor thepiston member at a limit position relative to the cylinder member, saidfingers being biased towards their latching positions; and

locking means to engage said fingers to positively lock the fingers attheir latched positions, said locking 7' means being releasable inresponse to fiuid pressure on the -side of the piston in the directionto retract the piston from the limit position.

2. A combination as set forth in claim l which includes discrete spacermembers interposed between the bearing portions of the successivefingers of the circumferential set of fingers, in the ring-shapedcavity, said spacer member being of the thickness of the saw cuts.

3. A combination as set forth in claim 1 in which said bearing portionsof the latch fingers protrude radially outward of the axis of thecircumferential set.

4. A combination as set forth in claim 1 in which said bearing portionsof the fingers protrude radially inwardly towards the axis of thecircumferential set; and

in which said bearing portions of the fingers are relieved to permit thebearing portions to rotate in said cavity as required for the latchingoperation.

5. In a fluidepressure actuator having a cylinder member and a pistonmember reciprocable axially therein, means for locking the piston at alimit position in said cylinder comprising:

a circumferential set of discrete latch fingers or" curved transversecross-section of the shape of longitudinal sections severed from acylindrical configuration by longitudinal radial saw cuts, saidcylindrical configuration having a concentric, generally ring-shapedenlargement at one end and a flange at the other end, the sections ofthe enlargement constituting bearing portions of the individual fingersand the sections of the flange constituting latch elements of theindividual fingers;

means fixed relative to one of said cylinder member and piston memberand forming a generally ringshaped cavity confining and journaling saidbearing portions of the fingers for swinging movement of the fingers,said cavity having ran annular concentric opening through which thelatch fingers extend;

latch means fixed relative to the other of said cylinder member andpiston member to engage said latch elements to releasably anchor thepiston member at a limit position relative to the cylinder member;

means to exert longitudinal pressure against the bearing ends of thelatch fingers to bias the fingersV towards their latching positions; and

locking means movable to a locking position to engage said fingers topositively lock the fingers at their latched positions, said lockingmeans being releasable in response to fiuid pressure on the side of thepiston in the direction to retract the piston from the limit position.

6. A combination as `set forth in claim 5 in which saidpressure-exerting means is Belleville spring means.

7. A combination as set forth in claim 5 in which said pressure-exertingmeans is huid-pressure means responsive to the iiuid pressure thatdrives the piston to the limit position.

8. A combination as set forth in claim 7 which includes spring meansbiasing said locking means towards its locking position.

9. In a fiuid-pressure actuator having a cylinder member and a pistonmember reciprocable axially therein, means for locking the piston at alimit position in said cylinder comprising:

a circumferential set of discrete latch fingers of curved transversecross-section of the shape of longitudinal sections severed from acylindrical configuration by longitudinal radial saw cuts, saidcylindrical configuration having a concentric, generally ring-shapedenlargement at one end and a radial fiange at the other end, thesections of the enlargement constituting bearing portions of theindividual fingers and the sections of the fiange constituting latchelements of the individual fingers;

`means fixed relative to one of said cylinder member and piston memberand forming a generally ring- CIK shapedcavity confining and journalingsaid bearing portions of the fingers for swinging movement of thefingers;

latch means fixed relative to the other of said cylinder member and'piston member to engage said latch elements to releasably anchor thepiston member at a limit position relative to the cylinder member;

a multiple-turn spring concentric with said set of latch fingers andyieldingly embraced by the fingers to bias the fingers towards theirlatching positions; and

locking means to engage said fingers to positively lock the 'fingers attheir latched positions, :said locking means being releasable inresponse to fluid pressure on the side of the piston in the direction toretract the piston from the limit position.

10. ln a fluid pressure actuator having a cylinder member and a pistonmember reciprocable axially therein,

means for locking the piston at a limit position in said cylindercomprising:

a circumferential set of latch fingers pivotally mounted on one of saidcylinder member and piston member;

latch means fixedly mounted on the other of said cylinder member andpiston member for engagement by said latch lingers to releasably anchorVthe piston member at a limit position; and

a multiple-turn spring concentric with said latch fingers and yicldinglyembraced by the fingers to bias the fingers radially outward towardstheir positions of engagement with said latch means.

' l1. In a duid-pressure actuator having a cylinder member and a pistonmember reciprocable axially therein, means for locking the piston at alimit position in said cylinder comprising:

two annular latch means fixedly mounted at the opposite endsrespectively of said cylinder;

two circumferential setsof latch fingers pivotally mounted respectivelyon the opposite ends of said piston member to engage said two fixedlatch means respectively to anchor the piston member at the two ends ofthe cylinder member selectively; and

fluid-pressure-responsive means mounted on said piston member to biassaid sets of latch fingers towards their latching positions in responseto the fiuid pressure against the piston member.

12. A combination as set forth in claim 11 in which saidfiuid-pressure-responsive. means includes auxiliary piston meansslidably mounted in said piston member for response to the pressuredifferential across the piston member.

13. A combination as set forth in claim 1 in which the latch fingers arebiased radially outward by annular spring means that is in Contact withthe inner circumference of the circumferential set of latch fingers andtends to expand' the circumferential set.

14. A combination as set forth in claim 13 in which the circumferentialset of latch fingers is formed with an inner circumferential groove toseat the annular spring means.

15. A combination as set forth in claim 9 in which said bearing portionsof the latch lingers are relieved to permit the bearing portions torotate in the ring-shaped cavity as required for the latching operation.

References Cited by the Examiner UNITED STATES PATENTS 2,295,961 9/42Meyer 92-5 2,434,828 1/48 Ashton et al 92-21 2,568,561 9/51 Perdue et al92-5 2,771,060 11/56 Allbright 92-24 2,813,518 11/57 Driskel et al. 9221 3,003,471 10/61 Bodem et al. 92-24 RTCHARD B. WILKNSON, PrimaryExaminer. FRED E. ENGELTHALER, Examiner.

1. IN A FLUID-PRESSURE ACTUATOR HAVING A CYLINDER MEMBER AND A PISTONMEMBER RECIPROCABLE AXIALLY THEREIN, MEANS FOR LOCKING THE PISTON AT ALIMIT POSITION IN SAID CYLINDER COMPRISING: A CIRCUMFERENTIAL SET OFDISCRETE LATCH FINGERS OF CURVED TRANSVERSE CROSS-SECTION OF THE SHAPEOF LONGITUDINAL SECTIONS SEVERED FROM A CYLINDRICAL CONFIGURATION BYLONGITUDINAL RADIAL SAW CUTS, SAID CYLINDRICAL CONFIGURATION HAVING ACONCENTRIC, GENERALLY RING-SHAPED ENLARGEMENT AT ONE END AND A FLANGE ATTHE OTHER END, THE SECTIONS OF THE ENLARGEMENT CONSTITUTING BEARINGPORTIONS OF THE INDIVIDUAL FINGERS AND THE SECTIONS OF THE FLANGECONSTITUTING LATCH ELEMENTS OF THE INDIVIDUAL FINGERS; MEANS FIXEDRELATIVE TO ONE OF SAID CYLINDER MEMBER AND PISTON MEMBER AND FORMING ACIRCUMFERENTIALLY CONTINUOUS GENERALLY RING-SHAPED CAVITY CONFINING ANDJOURNALING SAID BEARING PORTIONS OF THE FINGERS FOR SWINGING MOVEMENT OFTHE FINGERS; LATCH MEANS FIXED RELATIVE TO THE OTHER OF SAID CYLINDERMEMBER AND PISTON MEMBER TO ENGAGE SAID LATCH ELEMENTS TO RELEASABLYANCHOR THE PISTON MEMBER AT A LIMIT POSITION RELATIVE TO THE CYLINDERMEMBER, SAID FINGERS BEING BIASED TOWARD THEIR LATCHING POSITIONS; ANDLOCKING MEANS TO ENGAGE SAID FINGERS TO POSITIVELY LOCK THE FINGERS ATTHEIR LATCHED POSITIONS, SAID LOCKING MEANS BEING RELEASABLY IN RESPONSETO FLUID PRESSURE ON THE SIDE OF THE PISTON IN THE DIRECTION OF RETRACTTHE PISTON FROM THE LIMIT POSITION.